Sex-based physiological responses to a 750-m swim at critical velocity estimated by the three-parameter model

Critical Velocity (CV) is widely used to assess aerobic performance in endurance sports. Studies have compared protocols for CV determination in elite athletes. However, knowledge on the influence of the assessment protocol on CV and sex-based differences on metabolic responses at critical swimming velocity is limited.

This study aims to compare different protocols for determining CV in swimming among male and female triathletes and to compare sex-based differences in the metabolic and perceived exertion responses after swimming 750 m at CV estimated by the three-parameter model.

Highly trained amateur triathletes (12 men, 35.7 ± 11.0 years; 10 women, 38.1 ± 6.0 years) performed maximal swimming tests (50, 100, 200, and 400 m) to estimate Critical Velocity (CV). Each completed a 750 m swim at the CV determined by the three-parameter protocol (100-200-400 m), with monitoring of metabolic responses (lactate level and heart rate) and pain, dyspnea, and subjective perceived exertion.

The four-distance protocol yielded the highest CV in both sexes, whereas the protocol based on 92% of the 400 m time produced the lowest values (p < 0.001). After the 750 m swim, men showed higher ratings of perceived exertion (p = 0.005), pain (p < 0.001), dyspnea (p < 0.001), and blood lactate concentration (p < 0.001) than women.

The protocol used to determine CV significantly influences estimated values. Importantly, all findings related to physiological and perceptual responses during the 750 m swim are specific to the CV determined by the three-parameter protocol and should not be generalized to other CV determination methods. Under this protocol, CV may be associated with an exercise intensity approaching the severe domain; however, this interpretation should be made with caution.